The primary structure and tissue distribution of an amphibian neuropeptide Y

Sex-specific distribution of Neuropeptide Y (NPY) in the brain of the frog, Microhyla ornata

Neuropeptide Y (NPY) is involved in sex-specific behavioural processes in vertebrates. NPY integrates energy balance and reproduction in mammals. However, the relevance of NPY in reproduction of lower vertebrates is understudied. In the present study, we have investigated neuroanatomical distribution and sex-specific differences of NPY in the brain of Microhyla ornata using immunohistochemistry and quantitative real time PCR. NPY is widely distributed throughout the brain of M. ornata. We observed NPY immunoreactivity in the cells of the nucleus accumbens, striatum pars dorsalis, dorsal pallium, medial pallium, ventral pallium, bed nucleus of stria terminalis, preoptic nucleus, infundibular region, median eminence and pituitary gland of adult M. ornata. A higher number of NPY- immunoreactive cells were observed in the preoptic nucleus (p < .01), nucleus infundibularis ventralis (p < .001) and anteroventral tegmental nucleus (p < .001) of the female as compared to that of the male frog. Real-Time PCR revealed higher mRNA levels of NPY in the female as compared to male frogs in the mid-brain region that largely contains the hypothalamus. Sexual dimorphism of NPY expression in M. ornata suggests that NPY may be involved in the reproductive physiology of anurans.

Effect of neuropeptide Y on food intake in bullfrog larvae

Neuropeptide Y (NPY) is a potent orexigenic neuropeptide implicated in appetite regulation in mammals. However, except for teleost fish such as the goldfish and zebrafish, the involvement of NPY in the regulation of feeding in non-mammalian vertebrates has not been well studied. Anuran amphibian larvae feed and grow during the pre- and pro-metamorphic stages, but, thereafter they stop feeding as the metamorphic climax approaches. Therefore, orexigenic factors seem to play important roles in pre- and pro-metamorphic larvae. We investigated the role of NPY in food intake using bullfrog larvae including pre- and pro-metamorphic stages, and examined the effect of feeding status on the expression level of the NPY transcript in the hypothalamus. NPY mRNA levels in hypothalamus specimens obtained from larvae that had been fasted for 3 days were higher than those in larvae that had been fed normally. We then investigated the effect of intracerebroventricular (ICV) administration of NPY on food intake in the larvae. Cumulative food intake was significantly increased by ICV administration of NPY (5 and 10 pmol/g body weight, BW) during a 15-min observation period. The NPY-induced orexigenic action (10 pmol/g BW) was blocked by treatment with a NPY Y1 receptor antagonist, BIBP-3226 (100 pmol/g BW). These results indicate that NPY acts as an orexigenic factor in bullfrog larvae.

Characterization of the neuropeptide Y system in the frog Silurana tropicalis (Pipidae): three peptides and six receptor subtypes

Neuropeptide Y and its related peptides PYY and PP (pancreatic polypeptide) are involved in feeding behavior, regulation of the pituitary and the gastrointestinal tract, and numerous other functions. The peptides act on a family of G-protein coupled receptors with 4-7 members in jawed vertebrates. We describe here the NPY system of the Western clawed frog Silurana (Xenopus) tropicalis. Three peptides, NPY, PYY and PP, were identified together with six receptors, namely subtypes Y1, Y2, Y4, Y5, Y7 and Y8. Thus, this frog has all but one of the ancestral seven gnathostome NPY-family receptors, in contrast to mammals which have lost 2-3 of the receptors. Expression levels of mRNA for the peptide and receptor genes were analyzed in a panel of 19 frog tissues using reverse transcriptase quantitative PCR. The peptide mRNAs had broad distribution with highest expression in skin, blood and small intestine. NPY mRNA was present in the three brain regions investigated, but PYY and PP mRNAs were not detectable in any of these. All receptor mRNAs had similar expression profiles with high expression in skin, blood, muscle and heart. Three of the receptors, Y5, Y7 and Y8, could be functionally expressed in HEK-293 cells and characterized with binding studies using the three frog peptides. PYY had the highest affinity for all three receptors (K(i) 0.042-0.34 nM). Also NPY and PP bound to the Y8 receptor with high affinity (0.14 and 0.50 nM). The low affinity of NPY for the Y5 receptor (100-fold lower than PYY) differs from mammals and chicken. This may suggest a less important role of NPY on Y5 in appetite stimulation in the frog compared with amniotes. In conclusion, our characterization of the NPY system in S. tropicalis with its six receptors demonstrates not only greater complexity than in mammals but also some interesting differences in ligand-receptor preferences.

Autonomic control of glands and secretion: a comparative view

The autonomic nervous system together with circulating and local hormones control secretion from glands. This article summarizes histochemical and functional studies on the autonomic innervation and control of secretory glands in non-mammalian vertebrates, including secretion of saliva in the mouth and gastric acid in the stomach, secretion of enzymes and bicarbonate from the pancreas and gut wall, secretion of mucus in the gut epithelium and onto the skin, and salt secretion from salt glands and rectal glands. Cholinergic and adrenergic nerves, directly or indirectly, in combination with different types of peptidergic and other nerves appear to innervate gland tissues and affect secretion in all investigated species.

Terminal nerve-derived neuropeptide y modulates physiological responses in the olfactory epithelium of hungry axolotls (Ambystoma mexicanum)

The vertebrate brain actively regulates incoming sensory information, effectively filtering input and focusing attention toward environmental stimuli that are most relevant to the animal's behavioral context or physiological state. Such centrifugal modulation has been shown to play an important role in processing in the retina and cochlea, but has received relatively little attention in olfaction. The terminal nerve, a cranial nerve that extends underneath the lamina propria surrounding the olfactory epithelium, displays anatomical and neurochemical characteristics that suggest that it modulates activity in the olfactory epithelium. Using immunocytochemical techniques, we demonstrate that neuropeptide Y (NPY) is abundantly present in the terminal nerve in the axolotl (Ambystoma mexicanum), an aquatic salamander. Because NPY plays an important role in regulating appetite and hunger in many vertebrates, we investigated the possibility that NPY modulates activity in the olfactory epithelium in relation to the animal's hunger level. We therefore characterized the full-length NPY gene from axolotls to enable synthesis of authentic axolotl NPY for use in electrophysiological experiments. We find that axolotl NPY modulates olfactory epithelial responses evoked by l-glutamic acid, a food-related odorant, but only in hungry animals. Similarly, whole-cell patch-clamp recordings demonstrate that bath application of axolotl NPY enhances the magnitude of a tetrodotoxin-sensitive inward current, but only in hungry animals. These results suggest that expression or activity of NPY receptors in the olfactory epithelium may change with hunger level, and that terminal nerve-derived peptides modulate activity in the olfactory epithelium in response to an animal's changing behavioral and physiological circumstances.

Evolution of vertebrate neuropeptides

This review describes some of the most typical features in the evolution of neuropeptides. Neuropeptides are synthesized like other polypeptides and proteins, with an amino acid sequence determined by the DNA sequence of the corresponding gene. Mutations of bases in the coding regions of the DNA lead to changes in amino acid sequence, and explain the differences in amino acid sequence of a certain neuropeptide in different animal species. The more distantly related two species are, the more substitutions can be found in one and the same neuropeptide. The biologically active part of the neuropeptide is usually the most conserved part. Neuropeptides also form families of closely related peptides, where several members may occur in one animal species. This is due to gene or exon duplications followed by mutations. Gene splicing and posttranslational processing decides the gene product in a single cell. Difference in sequence may cause difference in function, but more often than not, members of a family appear to produce the same effect. Three neuropeptide families, the tachykinins, the neuropeptide Y family, and the vasoactive intestinal polypeptide/pituitary adenylate cyclase-activating peptide family will be described in more detail.

Characterization and distribution of neuropeptide Y in the brain of a caecilian amphibian

Neuropeptide Y (NPY) from the brain of an amphibian from the order Gymnophiona (the caecilian, Typhlonectes natans) was characterized. We cloned a 790 base pair cDNA encoding the caecilian NPY precursor. The open reading frame consisted of 291 bases, indicating an NPY precursor of 97 amino acids. Both deduced and isolated NPY primary structures were Tyr-Pro-Ser-Lys-Pro-Asp-Asn-Pro-Gly-Glu(10)-Asp-Ala-Pro-Ala-Glu-Asp-Met-Ala-Lys-Tyr(20)-Tyr-Ser-Ala-Leu-Arg-His-Tyr-Ile-Asn-Leu(30)-Ile-Thr-Arg-Gln-Arg-Tyr. NH2. In caecilian brain, we observed NPY immunoreactive cells within the medial pallium, basal forebrain, preoptic area, midbrain tegmentum and trigeminal nucleus. The prevalence of preoptic and hypothalamic terminal field staining supports the hypothesis that NPY controls pituitary function in this caecilian.

Neuropeptide families and their receptors: evolutionary perspectives

Examination of families of neuropeptides and their receptors can provide information about phyletic relationships and evolutionary processes. Within an individual a given signal molecule may serve many diverse functions, mediated via subtypes of the receptor which may be coupled to their transduction mechanisms in different ways. The rate of evolution of a peptide may reflect or be reflected in the rate of evolution of its receptor. For example, in the neuropeptide Y (NPY) family, pancreatic polypeptide (PP) shows significant structural diversity, while NPY is highly conserved. Molecular forms of a given subtype of NPY receptor that is selectively activated by NPY (Y1 or Y2 or Y5) are also highly conserved, but the subtype that is primarily activated by PP (Y4), shows remarkable diversity. Also, between receptor subtypes there can be remarkable diversity. This is evident in several neuropeptide families, where a neuropeptide sequence is highly conserved across a wide range of species but where the receptor homology of subtypes with species tends to be much lower than homology between species. For example, human and rat vasopressin are identical, but the human V(1)- or V(2)-vasopressin receptors are approximately 80% homologous with rat V(1)- or V(2)-receptors, but within humans or rats the V(1)-receptor is less than 50% homologous with the V(2)-receptor. Furthermore, duplication of an ancestral gene is thought to have led to the co-presence in eutherian mammals of oxytocin and vasopressin, which have maintained a close structural similarity, yet in many species the oxytocin receptor is only 30 to 50% homologous with vasopressin receptors. Thus it appears that there has been greater evolutionary pressure to conserve the signal molecule, than to conserve the structure of the receptor. Evaluation of the evolution of neuropeptides and their receptors may be useful in determining phyletic relationships. Traditional classification places the guinea pig as a hystricomorph rodent within the same order (Rodentia) as the muriform or myomorph rat and mouse. However, molecular analyses of polypeptides have led to the suggestion that guinea pigs belong to a distinct order. Analysis of several neuropeptide sequences and the Y4 receptor supports this view. In general terms for both neuropeptides and receptors, sequence homology reflects phylogeny and taxonomy as based on morphological features. Within the oxytocin/vasopressin family in which peptides and receptors have been characterised in invertebrate representatives as well as fish and amphibia in addition to mammals, the molecular diversity correlates well with evolutionary diversity.

Müller cells in the retina of the cane toad, Bufo marinus, express neuropeptide Y-like immunoreactivity

We have used light- and electron-microscopic immunohistochemistry to identify the presence of immunoreactivity to neuropeptide Y (NPY) within Müller cells in the retina of the cane toad, Bufo marinus. Müller cells containing NPY-like immunoreactivity (NPY-LI) were identified at the light-microscopic level by the coexistence with immunoreactivity to glial fibrillary acidic protein (GFAP) and at the ultrastructural level by their characteristic relationship to neuron cell bodies and processes. At the light-microscopic level, those cells which contained both NPY-LI and GFAP-LI usually had small cell bodies in the inner nuclear layer, while those cells which contained only NPY-LI were identified as large and small amacrine cells. The radially oriented primary processes in the inner plexiform layer and the vitreal end feet of GFAP-LI Müller cells also expressed NPY-LI. At the ultrastructural level, thin lamellar processes of Müller cells with NPY-LI enclosed some amacrine cell bodies in the inner nuclear layer and amacrine cell dendrites in the inner plexiform layer. These observations suggest that NPY-LI is localized in Müller cells in addition to two types of amacrine cells previously identified in the Bufo retina. This study provides the first evidence that glial elements in the vertebrate retina express NPY-LI.

Neuropeptides and their evolution

Neuropeptides are ubiquitous signalling molecules in all metazoans possessing nervous systems, from the simple nerve nets of the cnidarians to the immensely complex systems of mammals. While the discipline of peptide neuroendocrinology was born through the study of higher vertebrates, there now exists a plethora of information regarding neuropeptides and peptidic regulatory factors in invertebrates. Such phylogenetic studies have revealed that peptidic neurotransmission is of early evolutionary origin and that, while invertebrates have nervous systems which are simpler in terms of nerve cell number and organisation when compared with vertebrates, the complexity of the peptidic 'vocabulary' of invertebrate neurones is of a similar order of magnitude. Most research on invertebrate neuropeptides has been directed towards representative members of groups such as the insects and molluscs and it is only in recent years that efforts have been focused on the helminths (platyhelminths and nematodes). Here, the putative origins of peptidic transmitters is discussed and the current state of knowledge on helminth neuropeptides is reviewed. In order to place the study of helminth neuropeptides in an historical and conceptual perspective, methodological development and conceptual modifications in the disciplines of vertebrate and higher invertebrate peptide neuroendocrinology have been summarised.

Isolation and characterization of the Xenopus laevis cDNA and genomic homologs of neuropeptide Y

We have isolated Xenopus laevis cDNA and genomic clones encoding the neuropeptide Y (NPY) mRNA and gene using a probe from the human NPY gene. The longest open reading frame in the cDNA encodes a peptide 76% identical to human prepro-NPY and 73% identical to rat prepro-NPY. The putative mature Xenopus NPY (XNPY) peptide is 94% identical to both human and rat peptides. A genomic clone containing 422 base pairs of 5'-flanking sequences and the 5'-end of the mRNA was also isolated. Primer extension analysis was used to map the transcription initiation site of the Xenopus NPY gene. Comparison of the 5'-flanking sequences of the Xenopus laevis, human, and rat NPY genes resulted in areas of high conservation, including the TATA box and the CT box previously shown to interact with Sp1-like proteins. Distribution of the Xenopus NPY message was analyzed by Northern analysis and RNAse protection. XNPY transcripts were not detected in whole developing embryo RNA, but were detected in adult frog brain RNA. We have also conducted preliminary studies of the XNPY promoter, utilizing an XNPY/chloramphenicol acetyl-transferase fusion construct. This study has demonstrated that Xenopus NPY shares a high degree of identity to its human and rat counterparts and that this homology extends to the gene, which contains similar cis-elements positioned near the transcription start site.

Neuropeptide Y: a central regulator of energy homeostasis

Neuropeptide Y (NPY) is a 36 amino acid peptide belonging to the pancreatic polypeptide family of neuroendocrine hormones. It is the most abundant peptide yet discovered in the mammalian brain and is widely expressed by neurons in the central and peripheral nervous systems as well as adrenal medullary cells. Recently, a large number of studies have focussed on the potential roles played by NPY within the hypothalamus and pituitary with respect to the control of food intake and energy homeostasis. It is now clear that NPY is a potent stimulator of food intake in models of hyperphagia, that hypothalamic NPY also regulates sympathetic neural activity and it appears that NPY may also influence the glucocorticoid, growth hormone and thyroid hormone axes. Taken together, current data suggest that hypothalamic and pituitary NPY-expressing cells represent an important and critical site of integration of peripheral hormonal signals with regulation of energy homeostasis.

Rainbow trout (Oncorhynchus mykiss) neuropeptide Y

Neuropeptide Y (NPY) has been isolated from brain extracts of the rainbow trout (Oncorhynchus mykiss) and subjected to structural analyses. Plasma desorption mass spectroscopy estimated the molecular mass of the purified peptide as 4303.9 Da. Automated Edman degradation unequivocally established the sequence of a 36 amino acid residue peptide as: Tyr-Pro-Pro-Lys-Pro-Glu-Asn-Pro-Gly-Glu-Asp-Ala-Pro-Pro-Glu-Glu-Leu-Ala- Lys- Tyr-Tyr-Thr-Ala-Leu-Arg-His-Tyr-Ile-Asn-Leu-Ile-Thr-Arg-Gln-Arg-Tyr. The molecular mass calculated from this sequence (4304 Da) is consistent with that obtained by mass spectroscopy. The presence of a C-terminal amide was established by radioimmunoassay. Rainbow trout NPY is identical in primary structure to coho salmon (Oncorhynchus kisutch) pancreatic polypeptide (PP). These data may indicate that, in this group of salmonid fishes, a single member of the NPY/PP peptide family is expressed in both neurons and peripheral endocrine cells.

The primary structure of peptide Y (PY) of the spiny dogfish, Squalus acanthias: immunocytochemical localisation and isolation from the pancreas

1. Endocrine cells within islets, exocrine parenchyma and ductal epithelium in the pancreas of the spiny dogfish, Squalus acanthias, were immunostained with an antiserum to the C-terminal region of mammalian neuropeptide Y (NPY). 2. Radioimmunoassay of pancreatic extracts with the same antiserum detected immunoreactivity in the dorsal lobe (338 pmol/g) and ventral lobe (433 pmol/g). Reverse phase HPLC analysis of both extracts resolved a single immunoreactive peptide. 3. The primary structure of the isolated peptide was established as: YPPKPENPGEDAPPEELAKYYSALRHYINLITRQRY.NH2. 4. Peptide Y (PY) from Squalus acanthias is identical in primary structure to an NPY-related peptide isolated from the pancreas of Scyliorhinus canicula and has a 31/36 residue homology with porcine NPY. The 5 substitutions are highly-conservative.